Thermionic valves



NOV 5, i962 v. s. BAWDEKAR 3,662,989

THERMIONIC VALVES Filed April 25, 1960 VAMA/V JHA/VFQRA/V/ BAWDE/TAF?3,062,980 THERMHNlC VALVE Vaman Shantararn Eawdeitar, London, England,assigner to Associated Electrical Industries Limited, London, England, aBritish company Filed Apr. 25, i960, Ser. No. 24,547 Claims priority,application Great Britain Apr. 28, 1959 3 Claims. (Cl. 313-174) Thisinvention relates to thermionic valves of the kind having a cathode leadextending through the upper end of the valve envelope.

The invention has an important application in valves designed for use aseiiciency diodes in television receivers. Such valves have in the pastbeen subject to noise, the source 4of which has been diiiicult to trace.In such valves the potential of the cathode varies between fairly widelimits and is subjected to large voltage pulses. It is, therefore,necessary to provide, between the cathode and heater, insulation whichwill stand an appreciably higher voltage than that normally used inthermionic valves.

lt is ialso common practice with such valves to pass the cathode lead-inwire through the upper end of the valve envelope. During the gettering,deposition occurs on the internal surface of the upper part of theenvelope and it has been `found that in practice, during operation ofthe valve, there is a tendency for sparking to `occur between thecathode lead and the getter deposit during the occurrence of the highvoltage pulses and -this sparking has been found to cause the noiseabove referred to. lt is thought that this sparking is due to 4the factthat the getter film assumes a potential lying intermediate between thatof the cathode and the anode and hence there will be appreciablepotential diiferences `between the cathode and the getter deposit duringthe pulses. This arcing limits the maximum voltage at which 'such avalvel can be operated.

v The main `object of the invention is to provide an improvedconstruction enabling such valves to be run at higher voltages.

According to the present invention a valve of the kind referred to isprovided with an electrical Vconnection between the surface of theenvelope on which getter deposition occurs and a point `of lowpotential.

lt will be lappreciated that the getter deposit has a degree ofconductivity so that the connection need only be made to a localisedarea.

Preferably an electrical Iconnection is made between the getter depositand the cathode lead.

It has been found that such a connection appreciably reduces thetendency for sparking to occur and hence reduces the noise generated inthe valve.

ln order that the invention may be more clearly understood referencewill now be made to the accompanying drawing which shows an example of avalve embodying the invention.

In the drawing the reference 1 indicates a valve envelope, 2 is the topmica disc supporting the upper end of the electrodes of which 3 is theanode and 4 the cathode having an insulated heater 5 within it. Abovethe disc 2 is a getter ring 6 and between the getter ring 6 and the disc2 is a screen 7 to prevent getter deposition reaching the electrodes.

Extending upward from the cathode is a conductor strip 8 and to this inturn is connected a lead-in wire 9 extending through the upper end ofthe envelope. The getter deposition, which is indicated by the referencel0, occurs around the upper part of the envelope Patented Nov. 6, 1952and in accordance with the invention a conductor il is connected withthe upper end of the strip 8 and abuts against the internal `surface ofthe envelope so as to provide electrical connection between the getterdeposition and the strip 8.

Preferably the conductor il is resilient and is connected to the strip 8and lead-in wire 9 by welding at its mid point. With such a constructionthe valve may be assembled by pushing ythe electrode assembly upwardsinto the envelope. This will cause the conductor .il to press againstthe sides of the envelope and to bow, the bowing increasing the contactarea by causing the wire to lie along the inside face ot the envelope.The condutor il can, of course, be a wire of circular cross section or astrip.

yClearly the conductor il is only one way of carrying out the invention.

Whilst the embodiment `shown is the preferred Way of carrying out theinvention clearly it may be modiiied, or instance, the conductor lllcould be attached to the' wire 9 at a higher position provided it liesalong the inside of the envelope. lt may either be a wire `or strip.Instead of being connected to the cathode lead, the conductor 1l couldbe connected to any other lead extending from the electrode assemblywith a similar potential waveform to that of the top connection.

What I claim is:

l. A thermionic valve comprising an envelope, an electrode assemblylocated in said envelope, said elec trode assembly including at least ananode `and a cathode, a cathode lead extending through the end of saidenvelope, a gettering electrode located between the electrode assemblyand the cathode lead end of said envelope, and a grounding lead for thegetter deposit extending between a point of low potential and that partoi the inner face of the envelope between the gettering electrode andsaid cathode lead end of lthe envelope on which part the getter depositis formed.

2. A thermionic valve' comprising an envelope, an electrode lassemblylocated in said envelope, said electrode assembly including at least ananode and a cathode, a cathode lead extending through the end `of saidenvelope, -a gettering electrode located between the electrode assemblyand the cathode lead end yof said envelope and a grounding connectionfor the getter deposit extending between the cathode lead and that partof the inner face of the envelope between the gettering electrode andsaid cathode lead end of the envelope on which part the getter depositis formed.

3. A thermionic valve comprising an envelope, an electrode assemblylocated in said envelope, said electrode assembly including at least ananode and a cathode, a cathode lead extending through the epd of saidenvelope, a gettering electrode located betweh the electrode assemblyand the cathode lead end of said envelope and a grounding connection forthe getter deposit extending between the cathode lead and that part ofthe inner face of the envelope between thev gettering electrode and saidcathode lead end of the envelope on which part the getter deposit isformed, said grounding lead comprising a resilient strip extendingtransversely across the cathode lead to which it is attached at its midpoint so that the ends are pressed :resiliently `against the inner faceof the envelope.

Ishler June 24, 1952 Giacchetti May l2, 1953

